This invention relates to a material processing machine and particularly to a roll coater for applying liquids onto sheet material workpieces.
There are numerous instances in commercial material processing where liquids are coated onto sheet materials. For example, in the manufacture of headliners used in passenger motor vehicles such processes are frequently employed. Various techniques and designs of headliner manufacturing are presently known. In one process, an armature of soft flexible polyurethane foam is cut into thin sheets and coated with reactive components in a liquid state which polymerize to form a polyurethane which stiffens the substrate. Multiple layers of sheet materials may be coated and pressed together to provide adequate stiffness.
Various techniques for coating headliner substrates and other multi-layer assemblies are known. In one process, one liquid or two reactive components in liquid form are sprayed onto the sheet material workpiece as it passes along a conveyer through a processing station. Although spray coating operates effectively it is wasteful in that a substantial proportion of the material is lost as over-spray. The over-spray also may constitute an environmental hazard. Moreover, over-spray materials can interfere with the operation of other machinery and gives rise to increase maintenance costs.
Another process for coating substrates is known as roll coating. In this process, sheet material is fed between rolls which are coated with a liquid which transfers onto the workpiece. Although such machines generally operate satisfactorily they have a significant shortcoming; namely, they must be manually adjusted for a particular workpiece material thickness.
In conventional roll coaters, jack screw type separation adjustments are provided for the rollers. The separation between the rollers is especially important when soft open cell foam type materials are being coated. If the separation is excessively large, the coating rollers will not efficiently transfer the liquid onto the workpiece material. Conversely, if the separation is too small, the quantity of liquid retained by the workpiece is reduced since the rollers will "squeeze out" the transferred material. Accordingly, it is conventional practice to manually adjust the roller separation for a known sheet workpiece thickness. This requirement of manual adjustment makes the machines inflexible in terms of running parts of variable thickness. In certain production processes it would be desirable to provide a roll coater which can immediately and automatically respond to changes in workpiece thickness such that sheet material workpieces of varying thicknesses can be placed serially through the roll coater and each would receive an appropriate level of liquid retention.
Such desirable features of a roll coater are provided in this invention. The machine according to this invention features various mechanisms for providing an automatic adjustment characteristic. In one approach, one of the coating rollers is provided with an adjustment system including a moveable frame member which allows it to respond based on the pressure applied to it by the workpiece to adjust itself to an optimal roller separation. Despite the fact that the roll coater mechanisms are massive, the device according to this invention enables the rollers to respond to extremely minute forces exerted by the workpiece between the rollers, attributable in part to a precision counter-balancing of a moveable frame member which supports one of the rollers.
Another adjustment approach in accordance to this invention employs automatic pre-gauging in which a part is measured and a cam and follower device is actuated to set the separation between the coating rollers. In a hybrid arrangement, pre-gauging is used to set the coating roller separation within a range associated within a certain workpiece and the self-adjusting pressure actuated system described previously is employed to provide the final adjustment.
Irrespective of the approach used in accordance with this invention, parts of various thicknesses can be fed serially through the machine and a proper coating operation will be provided. This capability is especially advantageous where a wide range of material thickness are found in a finished item, for example in a headliner assembly in which a relatively thick soft polyurethane foam sheet is coated and thereafter reinforcing fiberglass mats or scrims and trim materials are coated to build up the various layers that define the headliner.
Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which this invention relates from the subsequent description of the preferred embodiments and the appended claims, taken in conjunction with the accompanying drawings.